01 - Pat chicken thighs dry with paper towels. Generously season both sides with salt, black pepper, smoked paprika, and dried thyme.
02 - Heat olive oil and unsalted butter in a large skillet or Dutch oven over medium-high heat. Arrange chicken thighs skin-side down and sear for about 6 minutes per side until golden brown. Transfer chicken to a plate and set aside.
03 - In the same pan, add sliced onions. Cook, stirring occasionally, until they become soft and golden, approximately 8 minutes. Add minced garlic and cook for 1 minute, stirring constantly.
04 - Sprinkle all-purpose or gluten-free flour over the onions. Stir and cook for 1 to 2 minutes to eliminate the raw flour taste.
05 - Gradually pour in chicken broth, whisking continuously to avoid lumps. Bring the mixture to a gentle simmer.
06 - Return chicken thighs to the skillet, skin-side up. Spoon some of the onion gravy over the chicken. Cover and simmer on low heat for 25 to 30 minutes until chicken is thoroughly cooked and the gravy is thickened.
07 - Taste the gravy and adjust salt and pepper as needed.
08 - Arrange chicken thighs on serving plates. Top with onion gravy and garnish with chopped fresh parsley if desired.